The present invention relates to joining of fine wires, and more particularly to a wire bonding method suitable for bonding a number of wires within a narrow area.
In a multi-layer wiring substrate, in general, a plurality of electronic parts are assembled at the high density. In such a substrate, when the circuit change becomes necessary due to the design change or the design miss, wires are added later so as to deal with the circuit change.
On the other hand, on account of the high-density assembling to the substrate or the miniaturization of the substrate, the bonding pad for bonding the repair wires becomes small in size and the repair wire becomes thin. Consequently, although most of such repair wires have been bonded by soldering conventionally, bonding by ultrasonic bonding such as described in "ELECTRONIC PACKAGING & PRODUCTION " FEBRUARY 1984, P. 124-P. 127 is performed in recent years.
Ball bonding is another connecting method similar to ultrasonic bonding. Ultrasonic bonding or ball bonding as described in Japanese patent application Laid-open No. 55-88348 or patent application Laid-open No. 55-12712 has been used as a bonding method of a lead wire for drawing an electrode of a semiconductor in the prior art. FIG. 9 shows a bonded state of a repair wire by the ultrasonic bonding method, and FIG. 10 shows a bonded state by the ball bonding method. In the bonding of the lead wire, only one wire is drawn per one bonding pad. However, in the multi-layer wiring substrate, a plurality of repair wires may be drawn from one connection pad.
According to the prior art, the bonded state of a plurality of repair wires on a bonding pad is shown in FIGS. 11 and 12. FIG. 11 shows the case by the ultrasonic bonding method, and FIG. 12 shows the case by the ball bonding method.
In the prior art, when a plurality of repair wires 2 are to be bonded on a bonding pad 1, since the plane bonding is performed as shown in the figure, the bonding pad 1 must have a prescribed size corresponding to the number of wires to be bonded. Consequently, if the connection pad 1 is very small, the wires of prescribed number cannot be bonded.